This invention relates to finger actuated switches, and more particularly to method and apparatus for protecting circuitry connected to tactile switches from an electrostatic discharge into the switch.
A programmable CATV converter includes a control unit having keyboard switches with electrical contacts connected through an associated signal processes to an earth ground reference potential. The processor is responsive to a signal from the control unit for selecting a particular television channel and converting the associated composite television signal to a prescribed RF frequency band prior to application to a subscriber's television set. The converter may also include MOS integrated circuitry comprising a microprocessor that is connected to the switches and ground. The microprocessor may store the identity of a number of channels that are pre-selected for viewing. Such integrated circuitry is particularly sensitive to electrostatic charge and may be destroyed by an electrostatic discharge induced during activation of the control unit. In a table top control unit, a viewer presses his finger on a large plastic button to activate an individual switch element of a matrix switch and select a prescribed channel for viewing. Although the plastic buttons insulate associated switch contacts from an electrostatic charge stored by the viewer's body when his finger touches the button, it results in a large and bulky control unit. In a small hand-held calculator-style control unit with a tactile or touch-type keyboard, there is only a sheet of Mylar.RTM. separating the electrostatic charge on a finger from switch contacts. The tactile matrix switch of another hand-held control unit included a thin flexible Mylar.RTM. face plate, having switch contacts on the back side thereof centered in associated blocks defined by orthogonal grid lines. In this matrix switch, an electrically conductive neoprene gasket-type shield was bonded onto the face plate along the grid lines and connected to ground. This protection shield proved unsatisfactory in a cold-dry climate in which a large electrostatic charge may be built up and stored, an electrostatic charge on a finger arcing through the Mylar.RTM. face plate rather than to the adjacent shield. An object of this invention is the provision of an improved electrostatic-discharge protected tactile switch.